FRIDAY, Nov. 1 (HealthDay News) -- Gazyva (obinutuzumab) has been approved by the U.S. Food and Drug Administration in combination with the anti-cancer drug chlorambucil for people with previously untreated chronic lymphocytic leukemia (CLL).

CLL is a progressive cancer of the blood and bone marrow. Some 15,680 Americans are likely to be diagnosed and 4,580 are projected to die from the disease this year, the U.S. National Cancer Institute estimates.

Gazyva is designed to bolster the immune system's ability to attack cancer cells, the FDA said in a news release. The agency said it granted the drug so-called "breakthrough therapy" status, since clinical evidence indicates it "may offer a substantial improvement over available therapies."

Approval was based on clinical studies of 356 people. Those receiving the Gazyva/chlorambucil combination had an average of 23 months of progression-free survival, compared with 11.1 months among participants who received chlorambucil alone, the FDA said.

The most common side effects of Gazyva were anti-drug reactions, a decrease in white blood cells, low blood platelets and/or red blood cells, muscle pain and fever.

Gazyva's label contains a boxed warning that it could trigger a "reactivation" of the
Hepatitis B virus, and it may increase users' risk of a rare neurological disorder called progressive multifocal leukoencephalopathy.